$\Delta U$ is equal to

Which of the following statements is correct?

Calculate the internal energy change of one mole of an ideal gas during an adiabatic free expansion process from a volume of $2 \ L$ to $5 \ L$.

Which one of the following equations does not correctly represent the first law of thermodynamics for the given processes involving an ideal gas? (Assume non-expansion work is zero)

The temperature of the system decreases in an

$A$ system gives out $x \ J$ of heat and does $y \ J$ of work on its surroundings. What is the internal energy change?